The present invention relates to a master cylinder reservoir assembly and more particularly, to a dual acting master cylinder reservoir assembly for use in a braking system of a motor vehicle.
Dual acting master cylinders are known and generally comprise a primary section and a secondary section each having a low pressure chamber and a high pressure chamber separated by a slidable piston. The primary and secondary pistons are aligned within a common bore and engage each other. A spring is compressed between the primary piston and the secondary piston such as to maintain a relative maximum separation between the two pistons. A retaining ring engageable by the primary piston retains the slidable components of the master cylinder assembly within the bore. A second spring acts on the secondary piston to bias the two pistons towards the retaining ring.
Both the primary and secondary sections of the dual acting master cylinder are supplied with hydraulic fluid by a reservoir which is carried on the master cylinder. The reservoir includes a pair of bayonets that are received within bosses integrally formed on the master cylinder, one each at the primary and secondary sections. A compensation port and a relatively small bypass hole provide fluid communication between each of the primary and secondary sections and the bayonets of the reservoir at each of the bosses.
Elastomeric seals are mounted on the pistons and allow a passage of hydraulic fluid from the low pressure chambers to the high pressure chambers but not in the reverse direction to compensate for return movement of the piston and for brake pad or shoe wear. The compensation ports generally provide fluid communication between the reservoir and the low pressure chambers of the primary and secondary sections of the master cylinder. The bypass holes generally provide fluid communication between the primary and secondary high pressure chambers and the reservoir when the pistons are in an at-rest position. When the master cylinder is actuated and the pistons moved to brake apply positions, the elastomeric seals move past the bypass holes so that the bypass holes are closed to the high pressure chambers.
The bypass holes are necessarily small to reduce the dead stroke of the dual acting master cylinder assembly, (where dead stroke is the loss of stroke between brake pedal movement and pressure build up). The use of a dual acting master cylinder and reservoir assembly in a motor vehicle provides two independent hydraulic circuits wherein a primary circuit is supplied by the primary section of the master cylinder through an outlet opening in communication with the primary high pressure chamber and a secondary circuit is supplied by the secondary portion of the master cylinder through an opening in communication with the secondary high pressure chamber.
The bayonets of the reservoir are generally provided as open as possible providing essentially unrestricted fluid flow and are sized to be received within the bosses of the master cylinder. Fluid flow between the reservoir and the master cylinder is therefore, determined by the size of the flow paths provided through the compensation ports and the bypass holes rather than by the openings in the bayonets themselves. An annular seal is generally provided on each of the bayonets to sealingly engage the internal bore of the bosses and to prevent fluid escape from the connection between the master cylinder and reservoir.
It is known to assemble the master cylinder and reservoir assembly, along with a power booster to provide a power assist to the manual application of force to actuate the master cylinder, into a motor vehicle and to connect the master cylinder outlet openings to the brake lines of a vehicle. Subsequent to installation within the vehicle, the braking system is filled with fluid through the master cylinder reservoir.
A typical means of filling the braking system with fluid is to introduce a pressurized fluid source into the reservoir and to open the bleed valves at the various wheel brake actuators of the braking system to effect the removal of air from the braking system and the introduction of operating fluid therein. It is also known that as an option to opening the bleed valves at the various wheel actuators it is possible to establish a vacuum in the braking system through the master cylinder and reservoir assembly and then to introduce fluid through the reservoir under pressure to completely fill the braking system without the need of opening the bleed valves at the various wheel brake actuators.
Through means of these known arrangements an effectively operating braking system and a method of assembling a braking system into a vehicle and filling it with fluid is known. The dual acting master cylinder arrangement results in a structure wherein either the primary section or the secondary section is itself adequate for bringing the vehicle to a stop should such operation be necessary.